The invention relates to a ceramic multilayer capacitor comprising a number of ceramic layers on the basis of barium titanate as well as a number of electrode layers of palladium or a silver-palladium alloy, the ceramic layers and the electrode layers being alternately stacked to form a multilayer, which is also provided with two external electric connections which are in contact with a number of said electrode layers. The invention also relates to a method of manufacturing this ceramic multilayer capacitor.
It is noted that the expression "on the basis of barium titanate" is to be understood to include, apart from pure barium titanate, materials in which the barium content is partly replaced by calcium, strontium or lead and/or by rare earth elements such as gadolinium and/or neodymium, and in which the titanium content is partly replaced by zirconium. In addition, the barium sites and the titanium sites of the material may be substituted with further suitable donor ions and/or acceptor ions, such as Mn, Bi, Nb etc. Such substitutions of barium and/or titanium are important to provide the ceramic material with properties which are necessary for the intended field of application of the capacitors.
Ceramic multilayer capacitors (CMCs) of the type mentioned in the opening paragraph as well as methods of manufacturing said capacitors are known, for example, from U.S. Pat. No. 4,882,651. In said Patent Specification, a description is given, more particularly, of a CMC which is provided with cover layers of a ceramic material. The chemical composition of the cover layers is identical to that of the ceramic layers situated between the electrode layers. In the known capacitors, use is made of cover layers whose grain size is larger than that of the ceramic layers.
It has been found that the known CMCs have an important drawback. Particularly in the case of capacitors comprising a large number of electrode layers (20 or more), the internal mechanical strength leaves much to be desired. Under specific conditions, this may cause delamination in the capacitor, leading to cracks between the electrode layers and the ceramic layers. This adverse effect takes place, in particular, if these capacitors are subjected to a thermal treatment. Such a thermal treatment occurs, for example, during soldering of the capacitors.
It is an object of the invention to reduce the above-mentioned drawback. The invention more particularly aims at providing a CMC in which said delamination is reduced so that the internal mechanical strength is increased. The CMC in accordance with the invention should also exhibit a long service life. The invention additionally aims at providing a method of manufacturing CMCs having a higher internal mechanical strength and a long service life.